This article, about legal efforts in several states to allow police to prevent Photographers from documenting police activity is frightening. And the laws are unconstitutional. They are content based, if not on their face, then in their application.
See the article here: http://m.gizmodo.com/5553765/are-cameras-the-new-guns
The NPPA has fought this kind of thing in the past and will continue to work to protect our rights.